Rahm carded a round of 67 to sit four shots off the lead held by Australian Lucas Herbert but was sweating after his outburst following a pulled tee shot on the par-three 15th.
A breach of the R&A's code of conduct can result in a shot penalty but Rahm faced no punishment, instead being given a warning later in his round by an official.
"I didn't think about it until I saw him (the official) on 17, and when he was walking up to me, I knew exactly what it was for, but I didn't think about it in the moment," Rahm said.
Known for his passion on the course, Rahm was asked if he was worried about further outbursts at Royal Birkdale over the weekend. "I shouldn't have reacted that way, but I did -- I mean, you guys are acting like it's every single hole. I get it. I had a moment," he added.
"I'm definitely more intense and passionate than a lot of the players out here, especially at work. But I wasn't thinking about it. It's not like I'm going to -- if I try to alter who I am too much, it might cost me a little bit on the course.
"But certainly shouldn't have moments like the one on 15; I get it."